Acoustic resistance



y 7, 1963 G. SCHENKEL 3,381,773

ACOUSTIC RESISTANCE Filed Feb. 21. 1967 INVENTOR.

GERRIT SCHENKEL AGENT United States Patent 3,381,773 ACOUSTIC RESISTANCE Gerrit Schenkel, Emmasingel, Eindhoven, Netherlands, assignor to North American Philips Co., Inc., New York, N.Y., a corporation of Delaware Filed Feb. 21, 1967, Ser. No. 617,543 Claims priority, application Netherlands, Mar. 30, 1966, 66-4,150 7 Claims. (Cl. 181-31) ABSTRACT OF THE DISCLOSURE An acoustic resistance for use in a microphone comprising a plurality of sintered metal grain pressed into a support body composed of a resilient synthetic resin.

The invention relates to an acoustic resistance for use in a device for converting acoustic vibrations into electric waves. More particularly, the invention relates to an acoustic resistance comprising a plurality of adjacent sintered metal grains contained in a supporting body and held together by the supporting body.

Such resistances are frequently used in microphones. They consist of a plurality of grains baked together by sintering. However, it is common practice hitherto to press the sintered grains in the form of an assembly into apertures in a mechanically hard material, such as iron or brass. These apertures are then completely filled by the grains. A disadvantage of this practice consists in that the grains are mechanically deformed when pressed into this material. As a result, the acoustic resistance value is also varied.

The invention is characterized in that the supporting body consists of a resilient synthetic resin.

By the use of this resilient synthetic resin, the aforementioned disadvantage is avoided. The sintered grains are not deformed during pressing so that the advantage is obtained that the acoustic resistance is not varied.

In an embodiment according to the invention, the supporting body has the form of a ring into which the sintered grains are pressed. In accordance with the required number, these rings can be slipped, for example, into a tube which is mounted afterwards in a microphone. Thus, with the use of the same kind of tube, various types of microphones can be provided with different tubular acoustic resistances.

The invention will now be described more fully with reference to the drawing in which:

FIGS. 1 and 2 are cross-sectional views of acoustic resistances in accordance with the invention, and

FIG. 3 is a longitudinal sectional view of a tube comprising a plurality of acoustic resistances.

In FIG. 1, a ring 2 of synthetic resin is secured on a steel ring 1. The ring 2 has several apertures 4 in which acoustic resistances are provided which have the form of sintered metal grains 3.

FIG. 2 shows another embodiment in which a metal tube with a flange 5 is provided on the inner side with a plastic tube 6. The tube 6 in turn is provided with an acoustic resistance 7 consisting of sintered metal grains.

In FIG. 3, a metal tube 10 is provided with several acoustic resistance units axially arranged in the tube at the required places.

3,381,773 Patented May 7, 1968 Each acoustic resistance unit consists of a plastic tube 11 in which an acoustic resistance 12 composed of sintered metal grains is provided.

What is claimed is:

1. An acoustic resistance member for use in an electroacoustic microphone comprising, a support body composed of a resilient synthetic resin material having an opening therein, and a plurality of adjacent sintered metal grains pressed together within said opening and held together by said support body so as to produce little or no deformation of the metal grains.

2. An acoustic resistance member as defined in claim 1 wherein said support body comprises a ring-shaped member into which the sintered metal grains are pressed.

3. An acoustic resistance member as defined in claim 1 wherein said support body comprises a ring-shaped member of resilient synthetic resin material having said opening therein, said acoustic resistance member further comprising a metal ring secured to said resilient ring-shaped memberand having an aperture therein aligned with the opening in said ring-shaped member to form a continuous sound passage therethrough.

4. In an electroacoustic microphone, the improvement comprising an acoustic resistance member comprising an elongate tube, a plurality of other tubes composed of a resilient synthetic resin material and mounted within said elongate tube in axially spaced relation, each of said resilient tubes being at least partially filled with a plurality of sintered metal grains pressed together within the tube and held together thereby.

5. In an electroacoustic microphone, the improvement comprising an acoustic resistance member comprising an elongate metal tube, a plurality of ring-shaped members composed of a resilient plastic material and coaxially mounted within said tube in axially spaced relation, each of said rings containing a plurality of sintered metal grains pressed together within the ring and held together thereby.

6. An acoustic resistance member for use in an elec troacoustic microphone comprising, a metal ring-shaped member having an aperture therein, a second ring-shaped member coaxially secured to said metal ring and composed of a resilient plastic material, said second ring having an opening therein aligned with said aperture and containing a plurality of sintered metal grains held together by the plastic member.

7. A method of forming an acoustic resistance within. an aperture of a support body composed of a resilient synthetic resin material comprising the following steps, sintering a plurality of metal grains together, and pressing said sintered metal grains into the aperture in said resilient support body.

References Cited UNITED STATES PATENTS 2,152,205 3/1939 Morrison 181--50 2,576,610 11/1951 Kunzog 138-41 3,115,207 12/1963 Wiggins 181-31 3,163,255 12/1964 Stryker 18150 3,163,256 12/1964 Lanning 181-56 3,270,834 9/1966 Bratt 181-36 3,293,379 12/ 1966 Gorike 179-1155 STEPHEN J. TOMSKY, Primary Examiner. 

